scholarly journals Model-independent and model-based local lensing properties of CL0024+1654 from multiply imaged galaxies

2018 ◽  
Vol 612 ◽  
pp. A17 ◽  
Author(s):  
Jenny Wagner ◽  
Jori Liesenborgs ◽  
Nicolas Tessore
Keyword(s):  
Gravitational Lensing ◽  
Cosmological Parameters ◽  
Linear Mapping ◽  
Small Scale ◽  
Parametric Modelling ◽  
Lens Model ◽  
Confidence Bounds ◽  
Multiple Images ◽  
Multiple Image ◽  
Model Independent

Context. Local gravitational lensing properties, such as convergence and shear, determined at the positions of multiply imaged background objects, yield valuable information on the smaller-scale lensing matter distribution in the central part of galaxy clusters. Highly distorted multiple images with resolved brightness features like the ones observed in CL0024 allow us to study these local lensing properties and to tighten the constraints on the properties of dark matter on sub-cluster scale. Aim. We investigate to what precision local magnification ratios, $\mathcal{J}$, ratios of convergences, f, and reduced shears, g = (g1, g2), can be determined independently of a lens model for the five resolved multiple images of the source at zs = 1.675 in CL0024. We also determine if a comparison to the respective results obtained by the parametric modelling tool Lenstool and by the non-parametric modelling tool Grale can detect biases in the models. For these lens models, we analyse the influence of the number and location of the constraints from multiple images on the lens properties at the positions of the five multiple images of the source at zs = 1.675. Methods. Our model-independent approach uses a linear mapping between the five resolved multiple images to determine the magnification ratios, ratios of convergences, and reduced shears at their positions. With constraints from up to six multiple image systems, we generate Lenstool and Grale models using the same image positions, cosmological parameters, and number of generated convergence and shear maps to determine the local values of $\mathcal{J}$, f, and g at the same positions across all methods. Results. All approaches show strong agreement on the local values of $\mathcal{J}$, f, and g. We find that Lenstool obtains the tightest confidence bounds even for convergences around one using constraints from six multiple-image systems, while the best Grale model is generated only using constraints from all multiple images with resolved brightness features and adding limited small-scale mass corrections. Yet, confidence bounds as large as the values themselves can occur for convergences close to one in all approaches. Conclusions. Our results agree with previous findings, support the light-traces-mass assumption, and the merger hypothesis for CL0024. Comparing the different approaches can detect model biases. The model-independent approach determines the local lens properties to a comparable precision in less than one second.

scholarly journals Model-independent and model-based local lensing properties of B0128+437 from resolved quasar images

2020 ◽  
Vol 635 ◽  
pp. A86
Author(s):  
Jenny Wagner ◽  
Liliya L. R. Williams
Keyword(s):  
Density Distribution ◽  
Confidence Intervals ◽  
Mass Density ◽  
Property Values ◽  
Free Form ◽  
Small Scale ◽  
Lens Model ◽  
Confidence Bounds ◽  
Multiple Images ◽  
Model Independent

The galaxy-scale gravitational lens B0128+437 generates a quadrupole-image configuration of a background quasar that shows milli-arcsecond-scale subcomponents in the multiple images observed with VLBI. As this multiple-image configuration including the subcomponents has eluded a simple parametric lens-model characterisation so far, we determined local lens properties at the positions of the multiple images with our model-independent approach. Using PixeLens, we also succeeded in setting up a global free-form mass density reconstruction, including all subcomponents as constraints. We compared the model-independent local lens properties with those obtained by PixeLens and those obtained by the parametric modelling algorithm Lensmodel. A comparison of all three approaches and a model-free analysis based on the relative polar angles of the multiple images corroborate the hypothesis that elliptically symmetric models are too simplistic to characterise the asymmetric mass density distribution of this lenticular or late-type galaxy. Determining the local lens properties independently of a model, the sparsity and the strong alignment of the subcomponents yield broad 1-σ confidence intervals ranging from 8% to over 1000% of the local lens property values. The lens model approaches yield comparably broad confidence intervals. Within these intervals, there is a high degree of agreement between the model-independent local lens properties of our approach based on the subcomponent positions and the local lens properties obtained by PixeLens. In addition, the model-independent approach efficiently determines local lens properties on the scale of the quasar subcomponents, which are computationally intensive to obtain by free-form model-based approaches. Relying on the quadrupole moment of each subcomponent, these small-scale local lens properties show tighter 1-σ confidence bounds by at least one order of magnitude on the average with a range of 9% to 535% of the of the local lens property values. As only 40% of the small-scale subcomponent local lens properties overlap within the confidence bounds, mass density gradients on milli-arcsecond scales cannot be excluded. Hence, aiming at a global reconstruction of the deflecting mass density distribution, increasingly detailed observations require flexible free-form models that allow for density fluctuations on milli-arcsecond scale to replace parametric ones, especially for such lenses as B0128, which have an asymmetric mass density distribution that may include localised inhomogeneities.

scholarly journals Generalised model-independent characterisation of strong gravitational lenses

2018 ◽  
Vol 620 ◽  
pp. A86 ◽  
Author(s):  
Jenny Wagner
Keyword(s):  
Time Delay ◽  
Gravitational Lensing ◽  
General Class ◽  
Deflection Angle ◽  
Lens Model ◽  
Gravitational Lenses ◽  
Source Position ◽  
Multiple Images ◽  
Model Independent ◽  
The Deflection Angle

Based on the standard gravitational lensing formalism with its effective, projected lensing potential in a given background cosmology, we investigated under which transformations of the source position and of the deflection angle the observable properties of the multiple images remain invariant. These observable properties are time delay differences, the relative image positions, relative shapes, and magnification ratios. As they only constrain local lens properties, we derive general, local invariance transformations in the areas covered by the multiple images. We show that the known global invariance transformations, for example, the mass-sheet transformation or the source position transformation, are contained in our invariance transformations, when they are restricted to the areas covered by the multiple images and when lens-model-based degeneracies are ignored, like the freedom to add or subtract masses in unconstrained regions without multiple images. Hence, we have identified the general class of invariance transformations that can occur, in particular in our model-independent local characterisation of strong gravitational lenses.

scholarly journals Multiply imaged quasars in the Gaia DR1

2017 ◽  
Vol 12 (S330) ◽  
pp. 59-62
Author(s):  
C. Ducourant ◽  
L. Delchambre ◽  
F. Finet ◽  
L. Galluccio ◽  
A. Krone-Martins ◽  
...  
Keyword(s):  
Cosmological Model ◽  
Gravitational Lensing ◽  
Cosmological Parameters ◽  
Global Strategy ◽  
Resolving Power ◽  
Multiple Images ◽  
Number Of Components ◽  
Gaia Dr1 ◽  
Observational Bias

AbstractBecause of to its exceptional resolving power, Gaia should detect a few thousands gravitational lensed systems. These consist in multiple images of background quasars. The estimated number of lens phenomena in the sky, however, depends on the cosmological model considered. By taking into account the observational bias that will restrict the detection of lensed quasars, identification of these up to a given limiting magnitude will constrain the cosmological parameters.We have investigated the known gravitationally lensed quasars present in the Gaia DR1, and found that a significant number of components of these systems have been measured and are present in the Gaia DR1 catalogue although quasi none of them have all their components detected. We additionally examined the immediate surroundings of QSOs from the large Quasar catalogue, LQAC3, and detected several configurations compatible with gravitational lensing phenomena. A more global strategy to systematically detect the potential candidates in the various releases of the Gaia catalogue is presented.

scholarly journals Generalized model-independent characterization of strong gravitational lenses V: reconstructing the lensing distance ratio by supernovae for a general Friedmann universe

2019 ◽  
Vol 490 (2) ◽  
pp. 1913-1927
Author(s):  
Jenny Wagner ◽  
Sven Meyer
Keyword(s):  
Time Delay ◽  
Cosmological Model ◽  
Gravitational Lensing ◽  
Distance Measure ◽  
Hubble Constant ◽  
Distance Measures ◽  
Gravitational Lenses ◽  
Confidence Bounds ◽  
Distance Ratio ◽  
Model Independent

ABSTRACT We determine the cosmic expansion rate from supernovae of type Ia to set up a data-based distance measure that does not make assumptions about the constituents of the universe, i.e. about a specific parametrization of a Friedmann cosmological model. The scale, determined by the Hubble constant H0, is the only free cosmological parameter left in the gravitational lensing formalism. We investigate to which accuracy and precision the lensing distance ratio D is determined from the Pantheon sample. Inserting D and its uncertainty into the lensing equations for given H0, especially the time-delay equation between a pair of multiple images, allows to determine lens properties, especially differences in the lensing potential (Δϕ), without specifying a cosmological model. We expand the luminosity distances into an analytic orthonormal basis, determine the maximum-likelihood weights for the basis functions by a globally optimal χ2-parameter estimation, and derive confidence bounds by Monte Carlo simulations. For typical strong lensing configurations between z = 0.5 and 1.0, Δϕ can be determined with a relative imprecision of 1.7 per cent, assuming imprecisions of the time delay and the redshift of the lens on the order of 1 per cent. With only a small, tolerable loss in precision, the model-independent lens characterisation developed in this paper series can be generalised by dropping the specific Friedmann model to determine D in favour of a data-based distance ratio. Moreover, for any astrophysical application, the approach presented here, provides distance measures for z ≤ 2.3 that are valid in any homogeneous, isotropic universe with general relativity as theory of gravity.

scholarly journals Automatic Selection of Multiple Images in the Frontier Field Clusters

2015 ◽  
Vol 11 (A29B) ◽  
pp. 779-780
Author(s):  
Guillaume Mahler ◽  
Johan Richard ◽  
Benjamin Clément ◽  
David Lagattuta ◽  
Vera Patricio
Keyword(s):  
Galaxy Clusters ◽  
Mass Distribution ◽  
Gravitational Lensing ◽  
Matter Content ◽  
Central Mass ◽  
Multiple Images ◽  
Multiple Image ◽  
Inner Region ◽  
Selection Of

AbstractProbing the central mass distribution of massive galaxy clusters is an important step towards mapping the overall distribution of their dark matter content. Thanks to gravitational lensing and the appearance of multiple images, we can constrain the inner region of galaxy clusters with a high precision. The Frontier Fields (FF) provide us with the deepest HST data ever in such clusters. Currently, most multiple-image systems are found by eye, yet in the FF, we expect hundreds to exist. Thus, in order to deal with such huge amounts of data, we need to develop an automated detection method. I present a new tool to perform this task, MISE (Multiple Image SEarcher), a program which identifies multiple images by combining their specific properties. MISE allows us to confirm or reject multiple images identified visually, but also detect new multiple-image candidates in MACS0416 and A2744, giving us additional constraints on the mass distribution in these clusters. A spectroscopic follow-up of these candidates is currently underway with MUSE.

scholarly journals A Model-Independent Characterisation of Strong Gravitational Lensing by Observables

Universe ◽  
2019 ◽  
Vol 5 (7) ◽  
pp. 177 ◽  
Author(s):  
Jenny Wagner
Keyword(s):  
Galaxy Evolution ◽  
Gravitational Lensing ◽  
Mass Density ◽  
Model Fitting ◽  
Mass Scale ◽  
Lens Model ◽  
Multiple Images ◽  
Strong Gravitational Lensing ◽  
Consistent Model ◽  
Local Properties

When light from a distant source object, like a galaxy or a supernova, travels towards us, it is deflected by massive objects that lie in its path. When the mass density of the deflecting object exceeds a certain threshold, multiple, highly distorted images of the source are observed. This strong gravitational lensing effect has so far been treated as a model-fitting problem. Using the observed multiple images as constraints yields a self-consistent model of the deflecting mass density and the source object. As several models meet the constraints equally well, we develop a lens characterisation that separates data-based information from model assumptions. The observed multiple images allow us to determine local properties of the deflecting mass distribution on any mass scale from one simple set of equations. Their solution is unique and free of model-dependent degeneracies. The reconstruction of source objects can be performed completely model-independently, enabling us to study galaxy evolution without a lens-model bias. Our approach reduces the lens and source description to its data-based evidence that all models agree upon, simplifies an automated treatment of large datasets, and allows for an extrapolation to a global description resembling model-based descriptions.

scholarly journals MIFAL: fully automated Multiple-Image Finder ALgorithm for strong-lens modelling – proof of concept

2019 ◽  
Vol 491 (3) ◽  
pp. 3778-3792 ◽  
Author(s):  
Mauricio Carrasco ◽  
Adi Zitrin ◽  
Gregor Seidel
Keyword(s):  
Simple Procedure ◽  
Lens Model ◽  
Proof Of Concept ◽  
Photometric Redshifts ◽  
Multiple Images ◽  
Mass Distributions ◽  
Photometric Redshift ◽  
Multiple Image ◽  
Strong Lensing ◽  
Blind Manner

ABSTRACT We outline a simple procedure designed for automatically finding sets of multiple images in strong lensing (SL) clusters. We show that by combining (a) an arc-finding (or source extracting) program, (b) photometric redshift measurements, and (c) a preliminary light-traces-mass lens model, multiple-image systems can be identified in a fully automated (‘blind’) manner. The presented procedure yields an assessment of the likelihood of each arc to belong to one of the multiple-image systems, as well as the preferred redshift for the different systems. These could be then used to automatically constrain and refine the initial lens model for an accurate mass distribution. We apply this procedure to Cluster Lensing And Supernova with Hubble observations of three galaxy clusters, MACS J0329.6-0211, MACS J1720.2 + 3536, and MACS J1931.8-2635, comparing the results to published SL analyses where multiple images were verified by eye on a particular basis. In the first cluster all originally identified systems are recovered by the automated procedure, and in the second and third clusters about half are recovered. Other known systems are not picked up, in part due to a crude choice of parameters, ambiguous photometric redshifts, or inaccuracy of the initial lens model. On top of real systems recovered, some false images are also mistakenly identified by the procedure, depending on the thresholds used. While further improvements to the procedure and a more thorough scrutinization of its performance are warranted, the work constitutes another important step toward fully automatizing SL analyses for studying mass distributions of large cluster samples.

scholarly journals Strong Lensing Cosmography in the Frontier Fields

2015 ◽  
Vol 11 (A29B) ◽  
pp. 801-803
Author(s):  
Eric Jullo ◽  
Ana Acebron ◽  
Marceau Limousin ◽  
Carlo Giocoli ◽  
Giulia Despali ◽  
...  
Keyword(s):  
Dark Energy ◽  
Cosmological Parameters ◽  
Simulated Data ◽  
Systematic Errors ◽  
Matter Density ◽  
Model Parameters ◽  
Lens Model ◽  
Multiple Images ◽  
Strong Lensing ◽  
Energy Equations

AbstractThe wealth of strong lensing features observed in the Frontier Fields clusters offers insights on the nature of dark energy. The large number of multiple-images systems with redshifts allows to simultaneously estimate the lens model parameters and the cosmological parameters involved in the distances calculations. In particular for the ΛCDM model, it is possible to estimate the matter density Ωm and the dark energy equations parameters wX. In this talk, I will present recent analyses of systematic errors based on Frontier Fields observed and simulated data.

scholarly journals When Darwin Met Einstein: Gravitational Lens Inversion with Genetic Algorithms

2005 ◽  
Vol 22 (2) ◽  
pp. 128-135 ◽  
Author(s):  
Brendon J. Brewer ◽  
Geraint F. Lewis
Keyword(s):  
Genetic Algorithms ◽  
Gravitational Lensing ◽  
Surface Brightness ◽  
Initial Study ◽  
Brightness Distribution ◽  
Gravitational Lens ◽  
Atmospheric Effects ◽  
Lens Model ◽  
New Approach ◽  
Genetic Algorithm Approach

AbstractGravitational lensing can magnify a distant source, revealing structural detail which is normally unresolvable. Recovering this detail through an inversion of the influence of gravitational lensing, however, requires optimisation of not only lens parameters, but also of the surface brightness distribution of the source. This paper outlines a new approach to this inversion, utilising genetic algorithms to reconstruct the source profile. In this initial study, the effects of image degradation due to instrumental and atmospheric effects are neglected and it is assumed that the lens model is accurately known, but the genetic algorithm approach can be incorporated into more general optimisation techniques, allowing the optimisation of both the parameters for a lensing model and the surface brightness of the source.

scholarly journals Encryption Algorithm of Multiple-Image Using Mixed Image Elements and Two Dimensional Chaotic Economic Map

Entropy ◽  
2018 ◽  
Vol 20 (10) ◽  
pp. 801 ◽  
Author(s):  
A. Karawia
Keyword(s):  
Logistic Map ◽  
Experimental Results ◽  
Encryption Algorithm ◽  
Current Work ◽  
Two Dimensional ◽  
Huge Number ◽  
Multiple Images ◽  
Encrypted Image ◽  
Multiple Image

To enhance the encryption proficiency and encourage the protected transmission of multiple images, the current work introduces an encryption algorithm for multiple images using the combination of mixed image elements (MIES) and a two-dimensional economic map. Firstly, the original images are grouped into one big image that is split into many pure image elements (PIES); secondly, the logistic map is used to shuffle the PIES; thirdly, it is confused with the sequence produced by the two-dimensional economic map to get MIES; finally, the MIES are gathered into a big encrypted image that is split into many images of the same size as the original images. The proposed algorithm includes a huge number key size space, and this makes the algorithm secure against hackers. Even more, the encryption results obtained by the proposed algorithm outperform existing algorithms in the literature. A comparison between the proposed algorithm and similar algorithms is made. The analysis of the experimental results and the proposed algorithm shows that the proposed algorithm is efficient and secure.

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